Multiple gun welder and control apparatus



July 7, 1970 G. A. ROBERTS 3,519,786

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MULTIPLE GUN WELDER AND CONTROL APPARATUS July 7, 1970 9 Sheets-SheetFiled Dec. 21, 1967 INVENTOR 601% 61. QM 504 {Pa/4 ATTORNEYS July 7,1970 G. A. ROBERTS 6 MULTIPLE GUN WELDER AND CONTROL APPARATUS 9Sheets-Sheet 5 Filed Dec. 21, 1967 MR Q $535k INVENTOR ml w 61 ATTORNEYSJuly 7, 1970 G. A. ROBERTS 3,519,736

MULTIPLE GUN WELDER AND CONTROL APPARATUS Filed Dec. 21, 1967 9Sheets-Sheet 4 c. A. ROBERTS 3,519,786

MULTIPLE GUN WELDER AND CONTROL APPARATUS July 7, 1970 9 sheets sheet 5Filed Dec. 21, 1967 ATTORNEYS cs. A. ROBERTS 3,519,786

MULTIPLE GUN WELDER AND CONTROL APPARATUS July 7, 1970 9 Sheets-Sheet 6Filed Dec. 21, 1967 INVENTOR 524 lm 3% 5 weu ATTORNEYS w WNb QM wpQb HmnWI G. A. ROBERTS July 7, 1970 3,519,786

I MULTIPLE GUN WELDER AND CONTROL APPARATUS 9 Sheets-Sheet 6 Filed Dec.21, 1967 RN MWW RVs r5555 k GL W {ATTORNEYS y 1970 G. A. ROBERTS3,519,786

MULTIPLE GUN WELDER AND CONTROL APPARATUS Filed Dec. '21, 1967 9Sheets-Sheet 9 BY [M000 AT TO'RNEYS United States Patent 3,519,786MULTIPLE GUN WELDER AND CONTROL APPARATUS Gordon A. Roberts, Ann Arbor,Mich., assignor to Warren Fastener Corporation, Mount Clemens, Mich., acorporation of Michigan Filed Dec. 21, 1967, Ser. No. 692,586

Int. Cl. B23k 9/20 US. Cl. 219-98 '18 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a multiple welding gun control apparatus foroperating a plurality of guns on a time sharing basis from a commonwelding controller and source of weld power having the capacity tooperate a single gun or weld applicator unit.

The guns are effectively scanned for selective access to the systemcontroller and power source through a series of time displaced orstaggered windows developed by the scanner. The guns are normallyblocked from system access except when a window opening is presented toa gun. If a gun is in a ready-to-weld or power requesting condition atthe time its window is opened or presented to the gun, it gains accessto the system, and the scanner is inhibited to maintain the window openfor substantially the duration of the welding cycle for the accessedgun. Upon or near the completion of the welding cycle, the scanner isenabled to close the window for the accessed gun and to presentsubsequent windows to the successive guns, which have been interlockedor blocked from access to the system during the time that the generationof the windows has been interrupted.

SUMMARY OF THE INVENTION The invention comprises a control apparatus forallocating a welding controller and transformer or source of power,having the capacity to operate a single welding applicator unit, to aplurality of selectively operable and conditionable applicator units ona time sharing basis. The control apparatus provides for each applicatorunit a separately addressable accessing control that permits access ofits conditioned applicator unit to the weld controller and power supplyto the exclusion of all the other units for substantially the durationof the weld controller cycle. Addressing of the accessing controls isaccomplished by scanning the several applicator units in a repetitiveand predetermined order and at a rapid rate having a period considerablyless than the duration of the weld controller cycle. An applicator unit,which is in a ready-to-weld or power requesting condition at itsscanning time or the time allocated for its access to the system, isoperatively connected {through its accessing control to the weldingpower supply and weld controller.

Upon access of a unit, the scanner is inhibited until completion of atleast the weld portion of the controller cycle, the other gun unitsbeing effectively locked out from gaining access to the weld controllerand supply system. Upon completion of the welding cycle, as determinedby the weld controller, the scanner is released to resume scanning andto enable access to the welding power supply and Weld controller throughthe accessing control next responding to the scanning of its conditionedapplicator unit.

As employed with a stud welding applicator unit equipped with automaticfeeding means for feeding and loading a stud into a gun, the multiplegun control apparatus permits several guns to be operated from the samesource and welding controller in time displaced welding cycles, butpartially overlapping feeding cycles such that a welding cycle may beinitiated for one gun during the ice feeding cycle of another gun thathas just completed a welding cycle.

Since the several guns are operated from the same source of weld power,safety controls are provided to protect an operator of an inactive gunfrom possible shock hazards while an accessed gun is drawing power fromthe system.

BACKGROUND OF THE INVENTION The invention is applied to a drawn ortransfer arc welding system of the type employed for stud welding ametallic fastener or stud to a workpiece. Such welders are characterizedby drawing a pilot arc of relatively low current intensity as the studis retracted from the workpiece by energization of a stud lift coil inthe stud applicator tool or gun. The pilot arc ionizes and lowers theresistance of the arc path through which the subsequently initiatedhigher intensity weld current is passed or transferred as or before thestud is plunged back toward the workpiece upon the timed de-energizationof the stud lift coil from the weld controller. Upon initiation of thehigh intensity weld current through the ionized arc path, the output ofthe supply source or transformer decreases to substantially its shortcircuit or zero voltage drop producing value, causing it to supplysubstantially all of its power through the established arc path, wherebyanother are path cannot be readily established from the same source ofpower and controlled from the same weld controller to supply controlledweld current to more than one gun at the same time.

Accordingly, it has been necessary heretofore to employ a separatecomplete welding station, including an independent source of weld energyor welding supply and controller, for each applicator unit, withconsequent increase in the capital equipment investment and no essentialsavings in the per unit cost of welding a stud as the number of weldingstations is increased.

In such prior systems, the several welding machines, essentially of thetransformer variety, are connected in parallel to the power mains orlines. Severe line loading results when the several stations are drawingweld power at the same time, causing a serious reduction in the voltageof the power mains that affects the weld energy and the quality of theweld.

The invention thus has as its basic purpose and object to reduce thecapital equipment investment and operating cost of this type ofequipment.

A specific object is to provide a multiple gun control apparatuspermitting several welding guns to be operated on a time sharing basisfrom the same weld controller and welding supply source of a powercapacity for operating a single welding unit.

A related object is to provide a multiple gun control apparatus inaccordance with the foregoing objects without duplication of majorcomponents and creating any noticeable interference to the operation ofthe several welding guns or applicator units.

Another object is to provide a multiple gun welding control apparatus inaccordance with the foregoing that distributes the weld loads or powerdemand from or on the system mains on a timing basis and without loadingbeyond that normally produced by a single gun or weld applicator unit.

Another object is to provide a multiple gun welding control apparatusoperable with and using logic type circuit elements.

Still another object is to provide a multiple gun control apparatus inaccordance with the foregoing that provides rapid access to the systemfor the first gun to request power therefrom and thereafter permits apredetermined order of accessing of the subsequent guns to the system.

Yet another object is to provide adequate safety precautions for theprotection of the operators from possible shock hazards resulting fromoperating multiple guns from a single or common source of weld power.

Another object is to provide apparatus in accordance with the foregoingfor a drawn arc stud welding system.

Another object is to provide a multiple gun welding and feeding controlapparatus that permits several guns to be operated from the same sourceof weld power and weld controller in time displaced welding cycles butoverlapping feeding cycles, such that a welding cycle may be initiatedfor one gun during the feeding cycle of another gun that has justcompleted a welding cycle.

The invention both as to its organization, structure and operationtogether with other aspects, features and objects thereof will beexplained more fully with reference to the accompanying description anddrawings, wherein:

FIG. 1 is a simplified block diagrammatic representation of the generalorganization of the multiple gun control apparatus of the presentinvention for a welding power supply and controller;

FIG. 2 is a representation of a stud welding gun or applicator unitindicating the basic electrical control elements associated therewith;

FIG. 3 represents the sequence of operations and functions related tothe line frequency, as developed by and provided from the weldercontroller for which the multiple gun control apparatus of the presentinvention is provided;

FIG. 4 is a diagrammatic and electrical circuit representation of thescanning unit employed in the multiple gun control apparatus of thepresent invention;

FIG. 4A is a status table of the conditions of the counter sectionemployed in the scanning unit of FIG. 4 for the multiple gun controlapparatus of the present invention;

FIG. 5 illustrates the occurrence and nature of timing pulses and thescanning windows at the indicated points in FIG. 4 as derived by thescanning unit of FIG. 4 employed herein;

FIG. 6 is a schematic electrical circuit of a representative one of theaccessing controls or gun control modules of the multiple gun controlapparatus of the present invention;

FIGS. 7 and 8 represent the schematic electrical circuit of theprincipal portions of the weld controller shared by several guns or weldapplicator units;

FIG. 9 is an electrical schematic circuit diagram of initiation controlcircuitry for the magnetic disconnect and sequence controls associatedwith the weld controller as modified for accommodation of a multiplicityof guns and including safety controls that have been added thereto;

FIG. 1 is an electrical schematic representation of the transformer andpower supply section of the welder, and also schematically illustrates arepresentative one of a plurality of gun contactor modules as providedfor each gun; and

FIGS. 11 and 12 are diagrammatic representations of the feeder memoryfeeder controller and of the feed control components operated from thecontroller and associated with a different one of the guns.

Although the principles of the invention are considered to be applicableto other forms of welding, sources of Weld energy, and controllers, theinvention will be described and illustrated in connection with a drawnarc welding controller such as the commercially available transfer arcClass 8992 (Type EQ2227G1) Stud Welder Controller, manufactured by theSquare D Company of Milwaukee, Wis. Such apparatus is suitable foroperating a stud welding gun applicator tool that may partake of thecharacter of those disclosed in US. patent applications Ser. No.369,115, filed May 21, 1964, and Ser. No. 485,007, filed Sept. 3, 1965,for Welding Apparatus, of common ownership herewith.

The principal components of such a welder controller are included inFIG. 1 and comprise a disconnect power section 10, a transformer section11 including the main weld transformer and pilot arc transformer, thewelder controller 12, and a contactor panel 13 through which pilot arcand weld current are supplied to a gun 14 under the control of thecontroller. Component 15 represents a feeder controller for an automaticfeeder apparatus that transfers and feeds a stud from a feed hopper (notshown) to be loaded in position in the gun.

The welding controller provides a plurality of control functions orevents, some of which have random initiation times and relativeoccurrences but all of which occur in a predetermined sequencereferenced to the line voltage frequency as indicated in FIG. 3 herein.These events inelude the energization of the magnetic relay disconnectof the power section and the sequence initiation relay of thecontroller, the starting of a pilot arc current through the gun, theenergization and the subsequent timed drop out of the gun lift coil, theinitiation of the flow of welding current, and the deenergization of therelay disconnect. These several functions constitute what may be termedthe electrical or weld cycle of the welder controller, starting with theenergization of the magnetic power disconnectcontacts from the closureof the trigger switch on a gun with a stud in place and touching thework, and extend over a period of several alternations of the 60-cycleline frequency to constitute an operational cycle for this form ofwelding controller of, say, approximately onetenth second duration,subject to some variation by the randomly initiated operations of someof the events thereof.

The total cycle time measured from the time a welding sequence isstarted for completing a weld from a gun to the time that that gun isready for the next weld sequence is shown in FIG. 3 as including theoperational cycle of the weld controller and that of the feedercontroller. The feeder cycle is initiated at or near the completion ofthe weld cycle and includes the time required to feed and transfer astud from a remote feed hopper to the gun and to load a stud intoposition in the gun. The feed and transfer time and the stud load timemay extend the total cycle time of a gun close to one second or more induration, depending upon the distance of the feeder from the gun', thesize of the stud and the mechanical characteristics of the loadingdevice on the gun.

The relay or power contactor for operating the line disconnect powercontacts is energized approximately one cycle of the line voltagevariation after the stud touches the work and the gun trigger switch isclosed. Approximately another cycle of the line voltage variationelapses due to the mechanical delay in contact operation before thepower contacts close to connect the weld transformer and pilot arctransformer to the line. The pilot arc transformer is connected to afull wave rectifier from which rectified current is supplied to the gunwhile the stud is still against the work.

The energization of the gun lift coil from the gun lift power supplycircuit is delayed slightly until after the start of pilot arc currentby a sequence delay relay that is energized with the power disconnectrelay and prevents the gun lift coil from being energized to start thestud retraction immediately with the pilot arc current. With pilot arccurrent flowing through the stud contacting the work, the subsequentenergization of the gun lift coil retracts the stud from the work andestablishes an arc path for the pilot arc current.

The welding controller includes a cycle counter and zero referencing orsynchronizing circuit that starts the counting of the AC. line cycles atthe first zero crossing point of the line voltage as it passes from apositive to a negative alternation, indicated at the point 0 in FIG. 3after the start of pilot arc current. At the cycle count of 2 from thecounter, a gun coil drop-out timing circuit contained in the weldercontroller is activated to time the drop out of the de-energization ofthe gun lift coil, that takes from, say, approximately 0.1 to 15.1milliseconds depending upon the mechanical characteristics of eachparticular gun. After the timing circuit has timed out, the gun coil isde-energized to plunge the stud, driven by a spring in the gun, towardthe workpiece.

A phase shifted signal, which is developed by a phase shift heat controlcircuit contained in the welder controller, is supplied at a time justafter that corresponding to the 2 /2 count status of the counter to agate firing circuit contained in the contactor panel. The gate firingcircuit fires the main weld SCR contained in a secondary line of theweld transformer to pass the weld current to the stud electrode terminalof the gun. The phase shift heat control circuit is adjustable toprovide the precise amount of welding current between the stud and theworkpiece to form a secure weld without overheating and damaging thestud or workpiece and effectively controls the conduction angle of themain weld SCR. The weld current SCR is turned on from the SCR gatefiring circuit to allow weld current, derived during the indicated halfcycle or alternation of the line voltage, to flow from the stud throughthe ionized path developed by the pilot arc to the workpiece. The startof the fiow of the weld current has been delayed or shifted under thecontrol of the phase shift heat control circuit from the start of thefirst positive alternation of line voltage occurring after the 2 countfrom the counter or corresponding to a count of 2 /2 cycles from thepoint 0. The welding current is shaped by an inductor which is in serieswith the secondary line and continues the directional flow of weldcurrent by discharging the inductive energy stored therein through thestud after the stud has contacted the workpiece at the stud plungepoint.

At the cycle count of 3, an end of weld sequence pulse from the countercauses the de-energization of the power disconnect and is also appliedto the feeder controller. The feeder controller controls an automaticfeeder associated with the gun to feed and load another stud in place inthe gun upon completion of the feeder cycle, the electrical circuitry ofthe weld controller is reset in preparation for another weld cycle fromthe loaded gun.

In accordance with the invention, the weld controller and weldtransformer are made available on a time sharing basis to a multiplicityof guns or weld applicator units as shown in FIG. 1, by provision of aseparate accessing control 18-(14) for each gun unit, a separatecontactor 13(1-4) for each gun unit, and a scanner 19 which effectivelyaddresses or scans the several gun units through their respectiveaccessing controls. A gun that is in condition to weld, i.e. requestingweld power, at the time its accessing control is addressed, is accessedor connected thereby to the weld controller, and the contactor for onlythat gun is selected or is conditioned for connection to the weldtransformer and the pilot arc supply.

The control apparatus makes the gun lift power supply, the gun liftdrop-out timing circuit and the phase shift heat control section of theweld controller available to several guns, each possessed of differentcoil drop-out time characteristics and different heat capabilitypeculiar to each gun. Those components of the weld controller gun liftcoil drop-out circuit and the phase shift heat control section, whichcontrol or provide the setting of the drop-out time and the percent heatcontrol 01' weld current, are duplicated and made available for each gunin its own accessing or gun control section 18 for selective independentinsertion in the gun lift drop-out circuit and the phase shift heatcontrol section of the weld controller through the accessing control ofa gun when it has been accessed to the weld controller and weldtransformer to the exclusion of the other gun units. The invention makesavailable on a timing basis the same weld power source, pilot arc supplysource, gun lift coil energizing source and drop-out timing circuit, andphase shift heat control circuit to a multiplicity of guns, at differenttimes.

While a common feeder controller could be employed in a slower actingsystem, the feeder controller is not time-shared in the presentembodiment of the invention in which separate feeder controllers areprovided for each gun. The use of separate feeder controllers enablesthe multiple gun control apparatus to operate the several guns in timedisplaced, but partially overlapping, total cycles in which a weldingcycle may be initiated for one gun while a feeding cycle issimultaneously taking place for another gun or guns that has or havecompleted their separate welding cycles. Thus, the number of weldingoperations that may be made over a given period of time is significantlyincreased.

A representative one of the gun accessing controls 18, also called a guncontrol module, is shown in FIG. 6, four of such controls being shown inthe four gun embodiment of the invention depicted herein. The number ofguns illustrated, howeevr, is not to be taken in a limiting sense, butto be determined instead by such factors as the duty cycle and thermallimit capability of the weld transformer and the relationship betweenthe number of welding operations imposed or required of a gun in aspecified period of time and the maximum duration of the entireelectrical welding or welding controller cycle.

With the exception of the stud on work transformer SOW which iscontained in the power supply section shown in FIG. 10 and is common toall of the guns and their accessing controls, each of the accessingcontrols 18 contains all of the components depicted in FIG. 6. Thesecomponents include a plurality of logic elements, which may be NORgates, typified by 28; a stud on work detector circuit 29; a pair ofreed contact type relays CRA and CRB having a plurality of contacts CR1through CR6; an electronic conduction latching device in the form of anSCR, labelled GCISCR, passing current to the gun lift coil in therepresentation of the gun 14 in FIG. 2; and the gun lift timingadjusting resistors 30, 31, 32 and percent heat control adjustingresistor 34 that are inserted respectively through relay contacts CR2and CR3 into the gun lift timing dropout circuit and into the phaseshift heat control pack of FIGS. 7 and 8 of the weld controller. The guncontrol modules constitute the interface equipment that serves to couplea particular gun or applicator unit to the time shared sequencecircuitry of the weld controller. The contacts of the reed relays CRAand CRB do the time share routing and selecting of timingcharacteristics peculiar to each gun.

The aforementioned NOR gates are conventional logic elements which maybe of conventional RTL form of the type shown in US. Pat. No. 3,243,652.A single input form of NOR gate is similar to the circuit enclosed inthe dashed and dotted rectangle I in FIG. 4. A multiple input NOR wouldinclude additional inputs, each containing a separate input resistor R,and connected to the point I of the circuit. This logic element providesa 1 level output therefrom only when all of the inputs thereto are at a0 level. If any or all of the inputs is or are l, the output is 0.

The potential levels providing operating signals to the logic controlledcircuitry in this unit are common and 20 volts, of which the commonlevel is referred to as 0 and the 20 volt level as 1. These potentiallevels, together with an Off-Return or logic reset signal are suppliedfrom a DO logic power supply module power supply PIM contained in thewelder power supply and transformer section, shown in FIG. 10. Asconstituted herein the welder power supply and transformer sectionincludes the main weld transformer EIT connected to the 460 v., 60 cycleA.C. mains through a manually operated disconnect labelled MAN DISC,fuse blocks 36 and 37, and magnetic or relay operated disconnectcontacts EIR, also referred to herein as the power contacts. Thissection also includes the pilot arc transformer PIT; a transformer P2Thaving three secondary windings P2TS1-P2TS3 of which P2TS1 correspondsto the aforementioned trans- 7 former SOW; and a constant voltagetransformer P3T which supplies the aforementioned power supply PIM andthe AC. power for the phase shift heat control pack in the weldcontroller.

FIG. 10 also shows in the dashed and dotted rectangle the form of atypical one of the contactors 13, one of which is provided for each ofthe guns to supply pilot arc and weld current to its corresponding gunwhen the control apparatus of the present invention has accessed thatgun and selected or prepared its contactor to receive power from thesystem. Each contactor as employed herein includes a main weld SCR,labelled ClSCR, that is gated from a gate firing module GFM to pass weldcurrent from the transformer through the aforementioned shaping inductorC1L to the negative or stud contacting electrode terminal of a gun, apilot arc SCR labelled CZSCR, and several relays C11CR, C2CR, and C3CRwhich have been added to the contactor section and control theconditioning of the gate firing module of the selected contactor and thegating of the pilot arc CZSCR to supply pilot arc current to the guncorresponding to the contactor of a selected gun.

The selection or accessing of a gun into the system is accomplished inconjunction with the scanner section 19 shown in FIG. 4 now to bedescribed. The scanner, also called a window generator herein, providesa sequence or series of time-spaced, non-overlapping or staggered pulsewindows, a different one of which is supplied over lines 40-1, 40-2,40-3 and 40-4 to a re-' spectively corresponding one of the accessing orgun control units. As shown in FIG. 4 the scanner is comprised of aclock or free-running multivibrator 41, a fourstage or state binarycounter 42, and a diode decoding matrix 47 having four decoding sectionsdesignated 48, 50, 52 and 54. Inhibiting means 56 in the form of asingle input NOR gate, constituting a switch, is also provided forstopping and restarting the clock under the control of the controller.

A form of counter suitable for use herein is described in US. Pat. No.3,243,652, having a pair of sections 44, 46 each of which has an inputand two outputs. The outputs from section 44 are designated as X and iand the outputs from section 46, as Y and Y. The circuit for a typicalone of the counter sections is shown in FIG. 8A of the aforementioendpatent.

The free-running clock 41 produces output pulses 62 as shown at A inFIG. 5, having a pulse repetition rate of 1000 or 1K Hz., for example,and having a pulse width or on-time of /2 milliseconds in durationseparated from the following pulse by a /2 millisecond offtime interval.Each time a pulse 62 is applied to the counter section 44, the unitchanges its output conditions. When the X output is at 0, the Y outputis at 1. When the next clock pulse 62 is applied, the X output changesto 1 and the X output changes to 0. The output from X is applied throughline 64 to the input of counter section 46. The outputs Y and Y remainin their initial conditions for the first two clock pulses and changecondition only when the output Ti changes from 1 to 0, or at every othertime a pulse is applied to unit 44.

The input to diode 66 of window 1, decoder 48 is from the Y output ofcounter section 46, and the input to diode 68 is from the i output ofcounter section 44, while the input to diode 70 is from the clockgenerator 41 through line 71. As indicated in the counter status tableof FIG. 4A, at the end of pulse No. 1, the if and outputs are both at 0level. At the same time, the input to diode 70 from the clock generatoris also at 0 level. A window 72 of half the width of the clock period,corresponding to the off time period of the designated clocking cycle,thus appears at the output of diode matrix 48 on line 40-1, signifying a0 potential level condition thereon, as indicated in FIG. 5.

The output of the decoder 48 is applied over line -1 to one of theinputs of a multiple input accessing Nor gate 10 of the gun #1 accessingcontrol of FIG. 6. Provided that all the other inputs to the gate arealso at 0 level, this completes a circuit from the +20 v. positive inputbias circuit, :which is similar to that shown in block 56 of FIG. 4, ofthe Nor gate 1C to the output of the matrix 48 being held at the 0 leveloutput of the X and Y terminals of the window generator and results inturning off the transistor in the gate. The output of the gate will beat the 20 v. level on the collector of the transistor therein,signifying a 1 logic level output from the gate. When any of the inputsto decoder 48 are at a 1 level, the 1 level appears at the output of thedecoder and is applied to its Nor gate 1C providing a negative (20 v.)signal to the input of the gate. A 1 level input to the Nor gateovercomes the positive bias on the input thereof and results in turningthe transistor on, thereby placing the output from the gate at common or0 logic level.

As indicated in FIG. 4, the inputs to decoders 50, 52, and 54 have atleast one 1 level input at the end of clock pulse 1 when the inputs todecoder 48 are all at 0 level. Hence, no windows appear at the outputsof decoders 50, 52 and 54, which supply a 1 level output therefrom tothe input of the accessing gate 1C of their respective gun controlunits. Accordingly, these units effectively are locked out from gainingaccess to the weld controller and power supply, and accessing of theseunits is prevented even though the units are in an otherwiseready-to-weld or demand requesting condition.

While equal on and off pulse times are shown for the clock oscillator,other complementing fractional periods and clock rates other than thatspecified may be employed. The off time of the clock pulse during whichthe window is generated need only be of suflicient width or timeduration to permit the logic and/or relay elements employed in thesystem to switch or operate and gain access to the system while thewindow is open. When a gun has gained access to the system, the windowis extended as later explained for a period corresponding approximatelyto the duration of the welder controller cycle. The use of a high orfast scanning rate in relation to the duration of the welding cycleenables a rapid accessing of the guns into the system.

In addition to the occurrence of a window at the input of an accessingNOR 1C of a gun control unit, the other inputs to that NOR must also bepresent, i.e., at 0, to place it in operative condition signified by a 1level output therefrom, for accessing its corresponding gun to thewelder controller and power supply. These conditions include the closingof the gun trigger switch 22 by the operator and a stud positionactuated angularity switch 24 in the gun, a stud-on-work detector signalindicating that the stud is on the work, and a signal from the feedermemory or controller circuit 314 of FIGS. 11 and 12 indicatir'rg thatthe feeder cycle, comprising the feed, transfer and loading of a stud toa gun, has been completed.

The gun switches 22 and 24 are connected in series, as indicated in FIG.9, and when actuated, supply ground from the common bus over line 35 toplace one of the inputs of the accessing NOR 10 of the control unit forthat gun at a 0 level. The closing of the trigger switch 22 andangularity switch 24 of a gun also supplies ground from the common busthrough the switches and line 38 to energize an initiation relay, asV21CR, which is shown in FIG. 9, and is associated with gun #1.Corresponding relays V22CR, V23CR, V24CR are provided for the other gunsin the four gun control apparatus illustrated herein. 7

Relay V21CR closes its contacts V21CR2 to energize the coil of a safetyrelay CllCR, which is physically contained in the contactor panel 13(1)of FIG. 10 for gun #1 and has its leads brought out therefrom over lines26, 27 for connection in the circuitry shown in FIG. 9.

A separate one of these safety relays C11CR-C41CR is provided for eachgun. Each of the safety relays is shown as having a set of normallyclosed contacts, as C11CR1, and a set of normally open contacts, asC11CR2, which are contained in the corresponding gun contactor circuitas shown. The contacts are discretely placed in the contactor circuitand serve to protect an operator of an inactive gun against shockhazards from leakage currents and possible malfunctions of the weldcurrent SCR (ClSCR) and pilot arc current SCR (C2SCR) when a gun isinactive and is not against the workpiece and another gun is drawingweld current from the common weld transformer.

The contacts C11CR1 when closed provide a near short circuit across thewelding cables at all times except during the interval of a weld cycleof a selected gun and prevent a possible shock hazard to the operator ofan unselected gun that may result from leakage current through or afailure of the weld current switch, CISCR. The weld SCR is a highcurrent device in which a substantial leakage current measured inmilliamperes is possible. Since power must be supplied to the weldingtransformer at all times that at least one gun is welding, then it ispossible to obtain a shock from an inactive gun. The safety switchcontacts C11CR1 prevent this possibility. In the event of a failure ofthe main weld SCR, the current passed through the safety contacts of aninactive gun would cause the fuse 129 to open in the secondary circuitof the main weld transformer.

The normally open contacts C11CR2 prevent the flow of leakage current toan inactive gun from the pilot are C2SCR and would also block the flowof the pilot are current in the event of a malfunction of C2SCR.

Upon the operation of the above mentioned relays and the opening of theshorting safety contacts. C11CR1 across the terminals of a selected gun,say gun #1, the stud-on-work signal can now be generated. This signal isdeveloped by the aforementioned stud-on-work detector circuit 29 inwhich the stud-on-work secondary transformer section P2TS1 is placed inthe detector circuit of and by a gun touching the work to provide powerto the transformer 80. A separate transformer of this character iscontained in the detector circuit of each accessing control unit. Thenegative output developed by the half wave rectifier output sectionconnected to the secondary of transformer 80 results in a negative or 1voltage level at point M connected to one input of the double input NORgate 1F. Gate 1F then supplies a level output to the stud-on-work inputof NOR 1C.

Assuming that the stud feeder apparatus associated with this gun hascompleted its operation, the feed cycle completion detector, which isserved by the feeder memory 314 shown in FIGS. 11 and 12, supplies a 0level signal over line 39 to the third input of NOR 1C. With theoccurrence of the window at the remaining input of the NOR 1C and theaforementioned other conditions, all of its inputs are at 0 level,whereby NOR 1C is placed in its access enabling condition represented bya 1 level condition at its output. This signal is supplied over line 82to the master memory section of the weld controller and throughconductor 83 to an inverter served by a single input NOR element 1B. NOR1B thus supplies a common level output potential over line 84 toenergize the reed relays CRA and CRB within the gun control unit andover line 85 to energize the relays CZCR and CSCR in the contactormodule in FIG. 10. corresponding to the selected gun. The energizationof the reed relays CRA and CRB results in the closing of the contactsCR1CR6 associated therewith, of which contacts CR5 provide an initiationhold common circuit over line 86 through the now closed contacts V21CR1to hold the initiation relay V21CR energized.

The 1 level output supplied from NOR 1C to the time shared weldersequence controller is supplied through diode 87 and over line 88 to aone-shot multi-vibrator, which is indicated at 89 in the weld controllersection of FIG. 7 and is comprised of NORS 3E and 3F, connected asshown. A single 1 level pulse of short duration is supplied from theoutput of the one-shot 89 and is applied to the master memory 94, whichis a switchable bistable device comprised of cross-coupled NOR gates 3Gand 3H, to place the output of 36 at 'a 0 level. NOR 3H receives a 0level signal from 36 and supplies its resulting 1 output over line 98 toturn on the PNP transistor 100 of the clock inhibit circuit 56 of FIG.4, resulting in holding one side of the clock generator at common levelpotential and in stopping the clock at the end of pulse #1. Line 98 isalso connected to the input of an inverter served by NOR 9F (FIG. 6)whose 0 output is supplied through contacts CR1 to provide a holdcircuit for the routing relays CRA and CRB in the accessing control unitand for the contactor selecting and conditioning relays CZCR and C3CR inthe contactor.

The above-described stopping of the clock with the selection of gun #1,thus etfectively locks out the remaining guns which then must wait untilthe clock is released to advance the counter and supply a 0 signal fromdecoders 50, 52 and 54 before any one of the remaining guns can haveaccess to the system. The scanning of the guns occurs in sequentialorder in FIG. 5 with only one gun being scanned at a time. Stopping. theclock efiectively extends the window 72 as indicated at 74 to a periodcorresponding to the operational cycle of the weld controller upon ornear the completion of which the clock is released as will be laterapparent.

A 1 level output from the master memory 94 of the controller section,shared by all of the guns, is also applied over line 99 to amplifierP3XA of FIG. 9. This amplifier is supplied with the Square D. WelderController and is a conventional commercially available A.C. amplifierthat effectively connects the L1 side of the A.C. line from thesecondary section P283 of transformer P2T to point H to permitenergization of the relays V1CR, EZCR and the magnetic disconnect relayElCR of FIG. 9. A weld-no-weld switch 122, shown in series with relayElCR, must be closed in order for this relay to be energized and, whenopen, enables the controller to be sequenced through a weld controllercycle without making a weld. The switches 124(1-4) are gun inhibitswitches, one of which is provided for each gun, and enable selectiveremoval of an associated gun from the system. Each inhibit switch iscontained in its own or corresponding gun control unit and is connectedto the associated elements shown in FIG. 9 over conductors 126, 127.

The energization of the disconnect relay closes its contacts EICR inFIG. 10 to supply 460 v. A.C. power to the welding transformer EIT andto the pilot arc transformer, which cannot be energized until this time.Relay E2CR, energized withrelays ElCR and VlCR upon the actuation ofamplifier P3XA from the master memory of the weld controller, closes itscontacts E2GR1 in FIG. 10 to provide a circuit through line 152 from thepilot are bridge rectifier 154 to the pilot arc switch constituted byC2SCR contained in the contactor section of the selected gun. ContactsCZCRl, closed by the previous energization of relay CZCR from NOR gate1B of the accessed gun control unit of FIG. 6, complete the gate circuitto C2SCR to allow C2SCR to fire. Inductance 158 and resistor 160comprise a smoothing circuit for filtering the output of the rectifiedD.C. pilot arc current.

At this time corresponding to point P in FIG. 3, gun #1 has acquiredexclusive access to the controller, its contactor has been selected, andpilot are current is being provided thereto. The stud in this gun isstill in contact with the work and must be retracted therefrom in orderto draw a pilot are between the stud and workpiece. Retraction of thestud is accomplished by the energization of the gun lift coil of theselected gun from the gun lift power supply shown in FIG. 8, in whichthe contacts V1CR1 have been closed by the aforementioned energizationof the sequence delay relay VlCR, the en- 1 l ergization and closure ofwhich has a random variation, like that of the and similarly energizedAC operated power contactor or main disconnect relay ElCR, as indicatedin FIG. 3.

The contacts V1CR2 shown in FIG. 7 of the sequence delay relay VICR havenow also closed to provide a 1 level input from the 20 v. source to theNOR gate 3M through RC filter network 164, which provides some slightadditional electrical delay to the signal passed through contacts V1CR2as well as affording some noise and contact bounce suppression. Theoutput from the filter is connected to an input of NOR gate 3M to supplya level signal over line 166 to inverting NOR 3]. The resulting 1 leveloutput from NOR 3] is applied over line 178 to turn on the PNPtransistor 181 of the gun lift energizing and drop-out timing circuit180 of FIG. 8, producing a pulse output when condenser 182 dischargesthrough line 184 to trigger SCR 186 contained in this circuit.

Firing the SCR 186 completes a circuit from the negative, commonreturned terminal of the full Wave bridge rectifier gun lift powersupply 190 over line 192, conductor 193, through the fired SCR 186,conductors 194, 195 and line 196 to one side of the gun lift coil 23 ofthe selected gun. Line 197 from the other side of the coil is appliedthrough GClSCR of FIG. 6 (also shown in dotted form in FIG. 8) and lines198 and 199 to the +80 v. terminal of the gun lift power supply, whichis shared by all of the guns. This energizes the gun lift coil of theselected gun, and the stud begins to lift away from the workpiece,drawing the pilot arc.

Another output from the aforementioned NOR gate 3] is applied over line174 to block or hold the one-shot multi-vibrator 89 off and prevent itfrom accidental retriggering during the weld cycle. The 0 level outputfrom NOR SM is also applied over line 168 to one of the inputs of amultiple input synchronizing NOR gate 3N, another input to which fromNOR section 36 of the Master Memory is also at 0. The other inputs toNOR 3N are supplied from the phase shift heat control peak 240 providedwith this controller and from the zero cross memory 172, comprised ofcross-coupled NORS 3P and 3R associated with the phase shift heatcontrol pack 240, which are decoding a line frequency signal to detect acurrent polarity change or line zero crossing, at which time 0 outputsare provided therefrom to the remaining inputs of NOR 3N. This placesall the inputs to NOR 3N at 0 level, and the resulting 1 level outputtherefrom is applied through line 173 to set another memory 176, whichis comprised of cross-coupled NOR gates 3K and 3L and is herein calledthe counter memory.

A 0 level output signal from NOR 3K of the counter memory 176 in FIG. 7is applied through line 200 to start the cycle counter SLM which issimilar to counter 42 FIG. 4 and is contained in the portion of thesequence controller shared by all of the guns. The cycle counterfunctions to count the cycles of the 60 cycle AC. power supplied to thewelding transformer after the gun lift coil has been energized and thepilot arc has been established, as described above. An output throughline 211 from the circuit of the NOR gates 3P, 3R and 3U 0f the phaseshift heat control pack 240 of the controller supplies a signal to thecycle counter at the instant when the alternating line voltage is at 0crossing potential. The 0 output from the counter memory 176 starts thecounter when the positive half cycle drops to 0 at point (0) of FIG. 3After the second cycle has been counted at point (2), a 0 output,representing a 2 count from the counter, is applied to the NOR gate 3X.A 1" output from the gate 3X is then applied through line 208 to turnOff NPN transistor 210, in the gun lift coil drop-out timing circuit ofFIG. 8, starting the gun lift coil drop-out time.

Gun lift coil 23 timing is determined by variable resistors 30, 31 ofFIG. 6 which are placed in the timing circuit of FIG. 8 through lines216, closed contacts CR2 of relay CRA, and line 220 which is connectedto resistor 222 in FIG. 8. The switch 33 in FIG. 6 cuts in or outresistor 32 to add 5 ms. delay to the timing range. When the transistor210 in the gun lift coil timing circuit of FIG. 8 turns off, unijunctiontransistor 228 turns on from the positive charge built up in condenser230. A positive voltage from unijunction 228 is applied through line 232to turn on SCR 234. Previously charged capacitor 236 discharges throughline 198 to the gun lift coil SCR (GISCR) driving its anode negative tostop conduction and de-energize the gun lift coil. The stud is thendriven under the power of a compressed spring in the gun and is plungedtoward the workpiece as indicated at the point SP in FIG. 3, designatedas Start Stud Plunge and shown herein as occurring prior to theinitiation of the weld current as described below.

Current supplied from the welding transformer EIT to weld the stud tothe workpiece is controlled by the aforementioned phase shift heat packcircuit 240 supplied with the controller. The operation and structure ofa form of phase shift heat control circuit is also described in US. Pat.No. 3,258,697. The heat pack unit 240 controls the initiation of theweld pulse and generates, at the appropriate zero crossing, the linesynchronization pulses supplied from the zero cross memory 172associated therewith and mentioned above.

At the cycle count of two, the inputs 260 and 262 to NOR gate SY of FIG.7 are at O and the input 266 is at 1. The input at 266 is determined bythe condition of the heat control memory 268, comprised of crosscoupledNOR gates 3S and 3T, associated with the heat pack. The memory 268 isswitched each half cycle by outputs of the heat pack at a timedetermined by the setting of the percent weld current resistor 34 ofFIG. 6. A resistor of this character is provided in each of theaccessing control units through which it is connected over line 246 toresistors 248, 250 and diode 252 in the heat pack and back over line 254to the closed contacts CR3 of relay CRA in FIG. 6. At point 272 of FIG.3, a phase shifted 1 output from the heat pack applied to the heatcontrol memory gates 3S and 3T produces a 0 output that is applied tothe input 266 of gate 3Y. All the inputs to gate 3Y are now 0, and a 1output is applied through line 273 to the gate firing circuit GFM inFIG. 10 in which contacts C3CR1 and C11CR3 were closed. When relays C3CRand CllCR, respectively, were energized, as previously described.

A gate firing module is contained in each contactor section 13(14)herein and is a commercially available component supplied with thewelder controller. Essentially, it is a pulse forming device fortriggering an .SCR, various forms of which are well known. Upon receiptof the logic triggering signal from 3Y, an output from the gate firingmodule applied between the gate and cathode elements of the main weldSCR, fires the main weld SCR (ClSCR), completing the circuit throughline and the stud and workpiece and line 128 to the secondary of thewelding transformer. A welding current, shifted in phase from the startof the corresponding voltage alternation, begins to flow through the arcbetween the stud and workpiece. The termination of the weld sequence issignalled when the cycle counter attains the count of 3, although theweld current continues to flow by reason of the aforementioned phaseshift and the effect of the inductor and discharge diodes, discussedbelow.

The stud contacts the workpiece at the stud plunge point labelled PP inFIG. 3, which is effectively the end of the weld current cycle. At thispoint or time, the resistance and voltage between the stud and workpiecedrops to a low value, and the inductor CIL in the activated contactorsection discharges through diode 288, the elments CIL and 288 serving toprotect the main weld ClSCR from current surges as Well as to shape theform and continue the flow of the weld current, as previously mentioned..The thyrector 290 protect the secondary of the welding circuit linefrom voltage surges. The voltage dividing circuit indicated at 292 isused to reduce transients from the transformer secondary.

. At the cycle count of three indicated at (3) in FIG. 3, a output fromthe cycle counter SLM of FIG. 7 is applied to NOR gate 3W. A 1 outputfrom gate 3W is applied through line 302 to reset the master memorygates 36 and 3H. A 0 output from the NOR 3H of the reset master memoryis applied through line 98 to remove the inhibiting potential from theclock oscillator 41 of FIG. 4, which restarts the flow of clock pulsestherefrom to continue the progressive scanning of the gun accessingcontrol units.

The 0 output from the master memory is also applied through line 99 tothe amplifier P3XA of FIG. 9, resulting in de-energizing relays ElCR,VICR, and E2CR and in the subsequent opening of magnetic disconnectswitch contacts E2CR1, V1CR1 and the various other contacts operated bythe above relays after the mechanical dropout time of these relays,whereupon the power to the welding transformer, pilot arc transformerand gun lift coil is shut off. The system is ready to start another weldcycle while the feeder memory is going through an operation as describedbelow controlling the feeding of another stud .to the just operated gun,gun #1.

The feeder memory controls the operation of the feed and transfer valvesof an automatic feeder (not shown) for automatically feeding andtransferring a stud to a gun and of a load valve,'which controls theloading of a stud in the gun of the character mentioned herein. Anadditional output from the feeder memory supplies a sustained 1 leveloutput voltage therefrom to the NOR of the accessing control unit forthe gun, with which the feeder is associated, to prevent" operation ofthe gun from the controller during a feed transfer and load operation.

The feeder memory 314 together with the DC. amplifiers 322 and 328operated therefrom are shown in the organization of FIG. 12, a completeand separate set of the units 314, 322 and 328 shown therein beingprovided for each gun. The amplifiers 322 and 328 are conventional D.C.drive amplifiers commercially available with welder controller equipmentof this character.

The composition of the feeder memory circuit member 314 is symbolicallyrepresented in FIG. 11 and comprises essentially a first NOR gateelement 340' supplying a NOR memory 342 formed of a pair ofcross-coupled NOR elements 344, 346. An input to NOR 344, labelled AutoFeed, is connected in a circuit over line 312 through the contacts CR4in FIG. 6 and line 308 to the output of NOR SW of FIG. 7, the outputfrom which at the cycle count of 3 starts the operation of the feedercircuitry by supplying a 1 level signal over the just described circuitto the Auto Feed input terminal of the feeder memory device 314. Anoutput from NOR 344 is supplied to an electronic timer 348 and theoutput from NOR 346 is supplied as a Feeder Memory Output signal to theinput of DC. amplifier 322 and over line 39 to the feeder input terminalof NOR 1C of accessing control 18(1) of FIG. 6 to prevent that NORelement from accessing gun #1 to the weld controller during the feedoperation taking place in gun #1, which has just completed its weldcycle. The DC. amplifier 322 (PZXA) provides a circuit through thesolenoid of the pneumatic feed valve indicated at 324 to the 20 v.source, energizing the solenoid and causing a stud to be fed andtransferred from the feed hopper.

The timer 348, which may be a conventional unijunction timing circuitand amplifier, supplies its output to another memory or bistableswitching element 350 formed of cross-coupled NORS 352 and 354. Theoutput of NOR 354 is supplied to the Load Output terminal from thefeeder memory connected to amplifier 328 (PlXA) to supply common levelpotential to one side of the solenoid of the pneumatic load valveindicated at 330 connected to the -20 v. source, thereby energizing thesolenoid to cause a stud to be loaded into position in the gun.

The output from NOR 352 is supplied to another timer 356 whose output isshown connected to one input terminal of NOR 346 and NOR 354. Anotheroutput, labelled Reset Output, taken from the capacitor diode circuitsupplied from NOR 352, is connected over line 332 and applied to the NORmemory gates 1D and 1B in FIG. 6 to provide a 0 output to NOR 1C andplace it in condition for the next weld operation at the end of the loadoperation.

In order to load the first stud into the gun, or in the event of afeeder malfunction, the manual load or recycle switch 25 located in thegun may be depressed to cause the selected feeder memory feed controllerassociated with that gun to energize the feed and transfer and loadvalves independent of the weld sequence.

As described above, the gun accessing control for the gun that has justcompleted a welding cycle is inhibited while the feeder cycle is takingplace for that gun. However, the restarting of the clock 41 permits thecounter 42 to continue the count to the decoder and to advance to itsnext state or count from the state or count in which it was left whenthe clock was inhibited by the previously accessed gun. The decodingmeans thus continues the development of the output window pulses in adefined order at the scanning rate of the clock until the next selectedand ready gun unit stops the clock while the latter unit has access tothe system welding controller and power supply. Thus, the several unitsare operable in overlapping total cycles, as earlier defined herein,during which a welding cycle for one gun may be initiated while thefeeding cycle is simultaneously taking place for another gun that hascompleted its welding cycle operation.

While a predetermined order of scanning has been described herein, otherscanning orders may be employed, including random scanning orders as maybe obtained with a random number control generator, for example.

What is claimed is:

1. Control apparatus for time sharing operation of a plurality of weldapplicator units from a single welding power supply of a capacity tooperate a single unit and from a controller providing a predeterminedsequence of control functions for operation of an applicator unit fromthe power supply,

said apparatus including a window pulse generator providing a series oftime displaced windows through which the weld applicator unitsselectively gain access to the power supply source and controllersystem,

selecting accessing means operable upon the presentation of a windowfrom the window generator to a weld applicator unit in a powerrequesting condition to connect that unit to the welding power supplyand controller system, and

means responsive to the access of a unit into the system to inhibit thewindow generator from generating and presenting successive windows tosubsequent weld applicator units for at least a portion of thepredetermined sequence of control function operations of the controller.

2. Control apparatus in accordance with claim 1 wherein the windowpulses provided from the window generator are of a duration and ratehaving a period considerably less than the duration of the predeterminedsequence of control operations provided from the controller.

3. Control apparatus in accordance with claim 1 wherein the windowgenerator includes a clock pulse generator, a counter activated from theclock pulse generator, and a decoder connected to the clock pulsegenerator and the counter.

4. Control apparatus in accordance with claim 3 wherein the clock pulsesare of a duration that is a fractional part of the clock period and thewindow pulses are generated during the complementary fractional portionof the clock period.

5. In combination with a welding apparatus power supply and a controllerthat provides a predetermined operating sequence of control functionscharacteristic of the particular form of welding for which the weldingapparatus is provided,

a plurality of welding applicator units,

means for time sharing the power supply and controller between theseveral units comprising,

a scanner for scanning the several applicator units at a rate at whicheach unit would be scanned several times in a period corresponding tothe duration of the sequence of control functions provided from thewelding controller, and

a plurality of selectively operable accessing means each connected tothe scanner and to a different one of the weld applicator units forconnecting its applicator unit to the controller and power supply inresponse to the scanning of its unit, said accessing means selecting andaccessing an applicator unit to the controller and power supply to theexclusion of the other units for a period of time no less than at leasta portion of the predetermined sequence of operations of the controller,whereby the same welding apparatus power supply and controller may betime shared by a plurality of weld applicator units.

6. In combination with a welding apparatus power supply and a controllerthat provides a predetermined operating sequence of control functionscharacteristic of the particular form of welding for which the weldingapparatus is provided,

a plurality of welding applicator units,

means for time sharing the power supply and controller between theseveral units comprising,

a scanner,

a plurality of selectively operable accessing means each connected tothe scanner and to a different one of the weld applicator units forconnecting its applicator unit to the controller and power supply inresponse to the scanning of its unit, said accessing means selecting andaccessing an applicator unit to the controller and power supply to theexclusion of the other units for a period of time no less than at leasta portion of the predetermined sequence of operations of the controller,whereby the same welding apparatus power supply and controller may betime shared by a plurality of weld applicator units, and

inhibiting means operable in response to and upon the access of ascanned conditioned unit to the weld controller and power supply throughthe accessing means for stopping and inhibiting the scanning means fromscanning the other units for the exclusive accessing period of anaccessed applicator unit.

7. The combination in accordance with claim 6 including means responsiveto the completion of the sequence of welding control functions providedby the welding controller for releasing the scanning inhibiting means.

8. In combination with a welding apparatus power supply and a controllerthat provides a predetermined operating sequence of control functionscharacteristic of the particular form of Welding for which the weldingapparatus is provided,

a plurality of welding applicator units,

means for time sharing the power supply and controller between theseveral units comprising,

a scanner for repetitively scanning the several weld applicator units ina predetermined coded order, and

a plurality of selectively operable accessing means each connected tothe scanner and to a difierent one of the weld applicator units forconnecting its applicator unit to the controller and power supply inresponse to the scanning of its unit, said accessing means selecting andaccessing an applicator unit to the controller and power supply to theexclusion of the other units for a period of time no less than at leasta por- 1 6 tion of the predetermined sequence of operations of thecontroller, whereby the same welding apparatus power supply andcontroller may be time shared by a plurality of weld applicator units.

9. The combination in accordance with claim 8 wherein the scanning meansrepetitively scans the several applicator units in sequential order.

10. In combination with a welding apparatus power supply and acontroller that provides a predetermined operating sequence of controlfunctions characteristic of the particular form of welding for which thewelding apparatus is provided,

a plurality of welding applicator units,

means for time sharing the power supply and controller between theseveral units comprising,

a scanner including a clock pulse generator and a counter activated fromthe clock pulse generator, and

a plurality of selectively operable accessing means each connected tothe scanner and to a different one of the weld applicator units forconnecting its applicator unit to the controller and power supply inresponse to the scanning of its unit, said accessing means selecting andaccessing an applicator unit to the controller and power supply to theexclusion of the other units for a period of time no less than at leasta portion of the predetermined sequence of operations of the controller,whereby the same welding apparatus power supply and controller may betime shared b a plurality of weld applicator units.

11. In combination with a Welding apparatus power supply and acontroller that provides a predetermined operating sequence of controlfunctions characteristic of the particular form of welding for which thewelding apparatus is provided,

a plurality of welding applicator units,

means for time sharing the power supply and controller between theseveral units comprising,

a scanner including a free-running clock pulse generator,

a binary counter activated from the clock pulse generator and having aplurality of counting outputs at least equal in number to the number ofweld applicator units, and a decoder connected to the clock pulsegenerator and the outputs of the counter to provide a scanningmanifestation in the form of a window pulse at a different timeallocated to each weld applicator unit, and

a plurality of selectively operable accessing means each connected tothe scanner and to a different one of the weld applicator units forconnecting its applicator unit to the controller and power supply inresponse to the scanning of its unit, said accessing means selecting andaccessing an applicator unit to the controller and power supply to theexclusion of the other units for a period of time no less than at leasta portion of the predetermined sequence of operations of the controller,whereby the same welding apparatus power supply and controller may betime shared by a plurality of weld applicator units.

12. The combination in accordance with claim 11 wherein the decodercomprises a plurality of gate matrices corresponding at least in numberto the number of weld applicator units to be scanned and each connectedto the clock generator and a different group of outputs of the counter.

13. In combination in accordance with claim 12 Where the gate matricesof the decoder are diode gates.

14. The combination in accordance with claim 12 wherein the clock pulsesare of a duration that is a fractional part of the clock period and thewindow pulses are of a duration corresponding to the complementaryfractional portion of the clock period.

15. In combination with a welding apparatus power supply and acontroller that provides a predetermined operating sequence of controlfunctions characteristic of the 17 particular form of welding for whichthe welding apparatus is provided,

a plurality of welding applicator units,

means for time sharing the power supply and controller between theseveral units comprising,

a scanner,

a plurality of selectively operable accessing means each connected tothe scanner and to a different one of the weld applicator units forconnecting its applicator unit to the controller and power supply inresponse to the scanning of its unit, said accessing means selecting anaccessing an applicator unit to the controller and power supply to theexclusion of the other units for a period of time no less than at leasta portion of the predetermined sequence of operations of the controller,whereby the same welding apparatus power supply and controller may betime shared by a plurality of weld applicator units, and the weldingapparatus being of the drawn arc stud welding type for stud weldingapplicator units each of which includes a stud lift coil selectivelyenergizable to retract a stud from a workiece and wherein the weldcontroller and power supply include means for energizing a lift coil,timing circuit means controlling the subsequent de-energization of alift coil and additional timing circuit means controlling the initiationof the weld current supplied through a stud applicator unit, and whereinthe accessing means for each of the plurality of applicator unitsincludes separate timing control elements that are peculiar to andcharacteristic of its associated applicator unit and are inserted in theaforesaid timing circuits of the weld controller when that applicatorunit is accessed thereto.

16. In combination:

a plurality of weld applicator units,

a source of welding power,

a welding controller providing a predetermined sequence of controlfunctions for effecting a welding cycle with an applicator unit fromsaid source of weld power,

parameter control means connected to the welding controller forspecifying the weld parameters for each applicator unit, and

a time sharing controller connected to the applicator units and to theparameter control means for effecting in time displaced welding cyclesconnection of the welding controller to one of the applicator units inaccordance with the welding parameters specified by the parametercontrol means for the particular applicator unit selected for welding.

17. The combination in accordance with claim 16 wherein the accessingmeans includes logic type elements including a NOR element responsive tothe scanner and a power requesting condition of an applicator unit.

18. The combination in accordance with claim 16 wherein the weldingapparatus includes a pilot arc power supply for supplying the currentfor the pilot arc drawn upon the retraction of a stud from the workpieceand wherein the same pilot arc power supply is shared by all of the weldapplicator units, but each at a different time.

References Cited UNITED STATES PATENTS 2,039,851 5/1936 Silverman 219-l14 X 2,505,808 5/1950 Strickland 307-41 3,051,825 8/1962 Rockafellow eta1. 219-108 JOSEPH V. TRUHE, Primary Examiner M. C. FLIESLER, AssistantExaminer U.S. Cl. X.R. 219-114; 3074l

